This invention relates to detectors, for example so-called electrochemiluminescence detectors.
Electrochemiluminescence (ECL) is a highly specific and sensitive detection protocol used in a wide range of analytical reactions, These can include bioassay in clinical diagnostics and high throughput screening for drug discovery.
In ECL, light emission is believed to originate from the solution in vicinity of the electrode surface where the reacting species (alternatively generated at the electrode surface via a series of potential steps into the oxidation and reduction diffusion plateaux) recombine by electron transfer to give rise to a luminescent excited state. It is generally found that the ECL spectrum correlates very well with the solution luminescence spectrum for the species involved.
One example of the process behind ECL is schematically illustrated in FIG. 1 of the accompanying drawings. Both tris(2,2xe2x80x2-bipyridyl) ruthenium (II) (TBRxe2x80x94also illustrated on FIG. 1 as Ru(bpy)3) and tripropylamine (TPA) are oxidised in aqueous solution at an anode face 10 of an electrode 40. The TPA is unstable and becomes deprotonated almost immediately to form TPAxe2x80x2. Subsequent electron transfer between TPAxe2x80x2 and TBR+ molecules leads to the formation of DPA (dipropylamine) and excited state TBR molecules (TBR*), which then relax radiatively to the ground state via an optical emission at a wavelength of 610 nm. In this reaction, although TPA is consumed, the TBR is recycled.
The arrangement shown in FIG. 1 is a so-called bipolar electrode design. In this arrangement, two end electrodes 20, 30 are connected to a power supply, with electrical continuity between them being provided by conduction through the aqueous electrolyte. Other intermediate electrodes (of which one, the electrode 40, is illustrated in FIG. 1) are not directly connected (i.e. wired) to the power supply but instead function as an anode on one face and a cathode on the other. So, every two adjacent electrodes and the intervening solution function as a reactor unit, with the overall apparatus forming a series connection of such reactor units. This arrangement is described in the book, xe2x80x9cElectrochemical Reactor Designxe2x80x9d, D J Pickett, Elsevier Scientific Publishing Company, 1979, and the chemical process is described in the article, xe2x80x9cSub-Microlitre Electrochemiluminescence Detectorxe2x80x94A Model for Small Volume Analysis Systemsxe2x80x9d, A Arora et al, Analytical Communications, 34, pp 393-395, 1997. This article also describes an ECL detection apparatus specifically for use with small sample volumes, the apparatus comprising a flow channel cut into an acetate sheet sandwiched between two blocks of poly (methyl methacrylate) or PMMA. Platinum foil strips are secured across the flow channel by the sandwich structure for use as the electrodes.
This invention provides an electrochemiluminescence apparatus comprising:
a reaction vessel;
means for generating an electric field within at least a region of the reaction vessel; and
one or more reaction electrodes disposed in the electric field region of the reaction vessel, the reaction electrodes being arranged to float in or on a solution in the reaction vessel.
In apparatus according to the invention, a novel type of electrode is used in an electrochemiluminescence technique, namely a floating electrode. This has many advantages over previous systems. The floating electrodes can be isolated or electrically short-circuited, and their use allows complex electrode patterns (such as extensive 1-, 2- or 3-dimensional electrode arrays) to be constructed on a very small physical scale, so allowing detection volumes to be very small while still providing useable emission light levels.
Potential uses of this technique and apparatus include immunoassays, DNA binding assays, receptor based assays, cell based assays, as a detector in liquid chromatography, for electrophoresis, electrochromatography in clinical diagnostics, enviroinental analysis, and in pharmaceutical and chemical research analysis.
The hydrostatically floating electrodes described above could also be electrically floating with respect to the means for providing an electric field, but need not be so. The invention also provides an electrochemiluminescence apparatus comprising: a reaction vessel; means for generating an electric field within at least a region of the reaction vessel; and one or more reaction electrodes disposed in the electric field region of the reaction vessel, the reaction electrodes being arranged to be electrically floating with respect to the means for generating the electric field.
Preferably, the apparatus comprises first and second supply electrodes connectable to an electrical power supply, the supply electrodes being disposed with respect to the reaction vessel and with respect to one another so that an electric current can flow between the electrodes through a conductive solution in the reaction vessel; the one or more reaction electrodes being disposed in the reaction vessel in a current flow path between the supply electrodes.
In this aspect of the invention, the reaction electrodes are electrically floating. That is to say, they are not connected directly to the power supply electrodes, apart from via their surroundings such as a conductive solution in the vessel. In this case, the reaction electrodes can be hydrostatically floating as well, could be fixed with respect to the vessel, or could be untethered but of such a nature that they sink.